A considerable development of membrane technology has taken place within recent years. The number of commercial applications of permeability separation processes, such as dialysis, ultrafiltration and reverse osmosis is increasing rapidly. One type of permeability separatory device -- i.e., "permeator" -- which has come into use employs membranes in tubular form. In one such type of device, the membrane is formed or emplaced as a skin on an interior or exterior surface of a rigid supporting tube which is grooved, perforated or has an open porous structure through which permeate can readily pass. For example, see U.S. Pat. Nos. 3,542,204; 3,581,900; 3,666,109; 3,708,069 and 3,734,297, which constitute the closest prior art known to the applicant.
Conventional tubular modules, as represented by the foregoing patents, are designed primarily for reverse osmosis. However, it has been a general practice to use these modules for ultrafiltration applications, disregarding the different requirements with respect to the distribution of the higher flow rates involved. Ultrafiltration (UF) applications, especially those involving tacky, viscous or gelpolymerizing solutions require very high flow rates to prevent blinding of the membrane surfaces by deposited solids or gels. Linear flow velocities of 10 to 25 feet per second are not uncommon.
For example, in a typical UF operation with a module of the present invention, a latex suspension has been found to require a velocity of 15 ft./sec. for continuous concentration by UF. This necessitates a flow rate of 8.5 gallons per minute through each one-half inch I.D. tube (membrane on the interior surface thereof) in the module. Thus, a seven tube module requires a total flow of almost 60 gallons per minute through whatever manifold means is employed. In order to achieve such flows, the manifold means must either be adpated to accommodate high pressures or must be sized much larger than in comparable reverse osmosis modules. Often, the large size connecting "U" turns and ancillary fittings approach the tube arrays themselves in cost and bulk.
The above listed U.S. Pat. No. 3,734, ' 297, which discloses the nearest prior art header design known of, is directed to a reverse osmosis module having a ladder-like configuration. The ends of a parallel array of permeable tubes are connected to cylindrical end members into which are inserted plugs having flow directing channels. In this module the feed solution is passed, under pressure, over a semi-permeable membrane layer on the outer surface of each tube and permeate is withdrawn from the interior of each tube through individual conduits which are passed through one end member and through the flow-directing plug therein, perpendicular to the axis of the end member. This design provides for facile replacement of individual permeator tubes but does not permit very efficient space utilization. A further disadvantage is that such modules are not well adapted to be ganged (joined with other such modules) end-to-end. Also, in order to change the relative flow rates or directions between two or more of the tubes in a given module, plug replacement is necessary. Moreover, since the module is not designed for permeation through the tube walls from the inside out, the difficulties of flow distribution inherent in the opposite mode of operation cannot be avoided.
U.S. Pat. No. 3,763,376 discloses a device in which a window and a light source are utilized, in conjunction with a haemodialyzer, to monitor dialysate for blood.